Thousands of Russian troops and Moscow-backed separatist fighters have been trying to capture the south-eastern Ukrainian city of Mariupol for almost a week.
Russian forces, who have been heavily shelling the port city of 400,000-500,000 people, have now cut electricity to residents.
The Donetsk-based separatist leader Denis Pushilin says his fighters are trying to encircle the city, though these troops are most likely an element of a larger Russian advance.
The battle is raging here because Mariupol sits in key strategic position on the Sea of Azov, dividing Russian forces on the annexed Crimean peninsula and Moscow-backed separatist troops in eastern Ukraine.
Russia has been trying to engage in amphibious landings of troops in the region for days with varying degrees of success, but if Moscow can capture Mariupol then it can establish a land-bridge between its forces in south-eastern Ukraine and Crimea.
But maybe more importantly, the city is also a major port. In normal times, ships here export grain around the world, but if captured the city would allow Russia to address its faltering logistics operation, which has seen dozens of tanks run out of fuel on Ukrainian highways.
